The mission of the Experimental Pathology Laboratory (EPL) is to provide a comprehensive array of histopathology services and expertise that enable UWCCC members to fully exploit the power of animal models of human cancer to reveal mechanisms that contribute to cancer development, progression, and responsiveness to therapies. EPL staff have extensive expertise in histology, histopathology, and cancer biology and together possess nearly 100 years of experience in cancer research. EPL has served a total of 99 UWCCC members during the current CCSG funding cycle, and between 43 and 58 unique members per year used EPL services during this interval. Both the number of members using EPL and the volume of services provided have increased since the CCSG was last reviewed and data from a 2016 survey of members indicate use will continue to increase. EPL prioritizes the following three aims: Aim 1 is to provide essential histology services to UWCCC members. Our members utilize a wide variety of animal models to address important questions pertaining to cancer etiology, prevention, and therapy. The EPL supports this research by providing essential histology services and expertise. Tissue specimens collected by UWCCC investigators are transported to the EPL where they are processed, embedded, sectioned, and stained according to the requirements of the investigator and our Standardized Operating Procedures. EPL offers common staining protocols, for example hematoxylin and eosin (H&E), and can perform virtually any special stain. Expert pathology consultation is provided by Dr. Ruth Sullivan, a board certified veterinary pathologist and EPL staff member. Aim 2 is to facilitate the molecular analyses of normal and neoplastic tissues. UWCCC members frequently evaluate expression, function, or localization of specific proteins as biomarkers or therapeutic targets. Upon request of a member, the EPL will develop and implement a custom immunohistochemistry (IHC) or immunofluorescence (IF) protocol that is specific to a protein of interest. Our members view this service as invaluable and over 70 unique IHC or IF protocols have been developed, optimized, and validated by EPL during the current CCSG funding cycle. Aim 3 is to provide histopathology expertise to UWCCC members and researchers. EPL staff members are available for walk-in consultation on sample preparation and handling or on operation of our Nikon fluorescence microscope for image acquisition. Dr. Sullivan provides monthly slide reviews and tutorials to UWCCC researchers free of charge. In addition, Dr. Sullivan is available for general pathology consults. Support from the CCSG allows us to provide UWCCC members with priority access to high quality histopathology services at costs below those of commercial laboratories as well as to provide expert consultative support at no cost to members.